In the lumber industry, it is well known that wood boards can be edge-glued to create larger panels of wood or face-glued to create beams.
It is also known that the scrap wood from various high-end lumber operations such as sawmill operations contain useful quantities of wood fibre which can be salvaged for lower-end lumber operations including the production of finger-jointed wood products. Finger-jointing processes cut usable wood fibre from scrap material and through shaping, gluing and clamping the ends of the scrap material create longer lengths or boards of lumber. The resulting longer boards built up from shorter lengths have advantages over equivalent lengths of solid, single piece lumber including 1) they will often be cheaper, 2) using certain glues, they will often have structural strengths equivalent to or greater than the strengths of an equivalent length of solid, single-piece lumber and, 3) longer, stable and straight boards of lumber (typically up to 62 feet) can be created.
As with solid, single-piece boards, finger jointed boards can be utilized as conventional lumber (ie for framing) or can be edge-glued and/or face-glued to create other lumber products. In particular, edge-glued lumber can be used to create slabs and face-glued lumber can be used to create beams.
Over the years, many techniques for finger jointing have evolved and continue to evolve both with respect to materials handling aspects of the process as well as with the gluing technology. For example, and with respect to gluing technology, in high speed operations producing finger jointed lumber, it is desirable that glue set times are fast in order to maintain high throughput levels. However, high-speed gluing requires that a careful balance be maintained between the glue set time and production speed to ensure that the glue sets during the clamping phase of assembly and not too early or too late in the process. In particular, a glue setting too early in the process will prevent proper assembly of the finger-jointed pieces whereas a glue setting too late will require longer clamping times.
Past glues have included phenol based glues which through a combination of moisture and heat-activation (microwaves) initiate the glue setting which in combination with the joint structure provide the resulting adhesive and structural strength at the joint. However, heat-activated glues utilizing microwaves require complex tunnels to both emit the microwaves and shield the plant from this radiation. In addition, the technology relating to products manufactured from phenol glues lend themselves to batch processes as opposed to continuous flow production by virtue of glue-setting apparatus. This is particularly true with respect to an edge gluing process.
As a result of some of the problems of phenol glues, quick-setting polyurethane glues have been developed and incorporated into high speed finger jointing operations. Polyurethane glues require moisture for setting which must introduced into the process and which therefore lend themselves to use with gluing green or wet-wood. Furthermore, polyurethane glues do not require the same specialized clamping and setting equipment and thus lend themselves to continuous production processes without the more complex glue-setting tunnels.
The equipment presently used in the continuous production of single lengths of lumber initially creates a finger joint on the ends of each piece of wood. Glue is applied to each finger joint and each piece of wood is moved onto a linear shuttle which accelerates successive pieces of wood against and into a leading piece of wood thereby causing adjacent finger joints on each piece of wood to interlock. At the end of the shuttle run, the assembled pieces are stopped against a first clamping surface, trimmed to length, moved sideways out of the shuttle run whereupon a longitudinal clamping pressure is applied to fully engage the finger joints. The resulting length of lumber is released from the clamp onto a horizontal deck to allow for final curing of the glue. As successive pieces of lumber are created, cut to length, moved sideways, clamped and released onto the horizontal deck, each piece of lumber is horizontally displaced across the deck. At the edge of the deck, each piece is removed for final processing, cleaning and packaging.
In the past, individual boards of single-piece or finger-jointed lumber could be subsequently assembled by edge-gluing to create slabs or face-glued to create beams in one or more separate operations to the milling or finger-jointing processes.
For example, past edge-gluing processes apply glue to the edges of adjacent boards and clamp and press adjacent boards together while the glue is curing to form a slab. However, such processes are generally non-continuous, slow and/or labour-intensive which results in higher production costs than could be achieved if the slab was created as part of the initial milling or finger-jointing assembly process.
Accordingly, there has been a need for an edge or face gluing process and apparatus that provides the continuous assembly of lumber into edge-glued or face-glued slabs at high speed and pressure.
Another problem with past wood-gluing equipment is the clamping pressure profile applied to a growing slab. That is, in past systems which may apply a clamping pressure across a growing slab, as each successive board is added to the growing slab, there are substantial changes in the clamping pressure as linear shuttles advance and retreat. Accordingly, there has been a need for an wood-gluing process and apparatus which provides a high, continuous clamping pressure across the width of the slab while additional boards are being prepared and added to the slab.
Further still, there is a distinction between panels manufactured for furniture and for construction. In particular, construction grade lumber requires that the strength of any glued joint is greater than that of the wood whereas furniture grade wood does not require the same joint strength or integrity. In manufacturing construction grade lumber from glued pieces of wood, either finger jointed or edge-glued, in order to ensure that there is maximum joint strength, high clamping pressures are required to ensure proper glue penetration into the wood during the curing cycle and particularly in continuous flow operations. Such techniques are required to have lumber certified by certification agencies.
Past edge-gluing systems have not solved these problems. A review of the prior art has revealed U.S. Pat. No. 6,025,053 and U.S. Pat. No. 5,888,620 (Grenier) which disclose a process for adhesively bonding finger jointed lengths of wood in side-by-side relationship to form boards; U.S. Pat. No. 4,314,871 (Weinstock) which discloses a method and apparatus for laminating timber to form laminated beams; U.S. Pat. No. 4,565,597 (Schulte) which discloses a method for producing a veneer web which are bonded side-by-side to form a veneer web; U.S. Pat. No. 5,679,191 (Robinson) which discloses a method and apparatus of fabricating trailer flooring via an edge-gluing process and U.S. Pat. No. 3,927,705 (Cromeens), U.S. Pat. No. 4,128,119 (Maier), U.S. Pat. No. 4,941,521 (Redekop) and U.S. Pat. No. 5,617,910 (Hill) which each disclose finger jointing apparatus per se.